This invention relates to prosthetic devices and more particularly to such prostheses that are formed as a composite that includes a layer or coating of porous polymeric material.
Most prostheses are fixed to the skeletal system by impacting a stem in the medullary canal of an appropriate bone or by mechanically fixing the device with a "bone cement" such as polymethylmethacrylate. However, these methods are not completely satisfactory because the devices tend to loosen upon impact or by use over a long period of time.
A phenomenon known as tissue ingrowth has been used in attempts to anchor prosthetic devices in place. Tissue ingrowth is where human tissue such as bone, tendons, blood vessels, etc., continues to grow after a prosthetic device is in place and will actually grow into and fill openings adjacent to the tissue. It has been recognized that ingrowth can be used to anchor prosthetic devices in place.
Polymeric materials such as polyethylene and polypropylene have been found to be suitable for use in prosthetic devices because of their biocompatibility and strength. Porous matrices of polyolefins and other polymers have been developed recently. These porous materials were evaluated successfully as a means of anchoring prosthetic devices.
A porous form of polyethylene and polypropylene has been developed. It has been suggested that this material be used for prosthesis attachment. However, since physical properties of porous materials tend to vary considerably with pore size and internal pore geometry, it was not know to what extent and how those materials could be used in prosthetic devices or what the essential physical characteristics of the material are for any such use.